MOVEMENTS OF THE LAKE WATERS 491 



no return current so well marked as in the other lakes of the Great Lakes 

 system has been found. The probability seems to be that in part it 

 breaks up into smaller whirls along the great pockets of the coast on 

 either side of the general current, and that a considerable body of water 

 is returned as an undercurrent. The general east flowing current is very 

 slight, probably never exceeding 12 miles per day, more frequently being 

 much less than this. The currents of the general circulation and the 

 return currents are too feeble to transport even the finest sand which 

 occurs along the beaches. They must, however, assist in the distribution 

 of the finest silts and clays over the bottoms of the lakes. 



At points along the shores of the lakes, streams other than the main 

 rivers of the system enter, and their currents may at times, especially 

 during the period of spring floods, affect the waters of the lakes for a 

 short distance from the shore. At this time one can often see the dis- 

 colored waters flowing through the clear lake waters for a mile or more, 

 rarely over 2 miles from the mouth of the discharging stream. This dis- 

 coloration is produced by the silts in suspension, but even these are 

 quickly deposited in the relatively more quiet waters of the lakes. Except 

 in the immediate vicinity of the mouths of the streams in question, these 

 currents have no effect in modifying the lake shores. The direction that 

 they turn in flowing through the lake waters, except for the first few 

 yards of their course after leaving tlieir outlets, is determined wholly liy 

 the direction the lake waters at their point of discharge happen to be 

 moving at the time. 



With regard to the surface currents produced hj the prevailing winds, 

 their general direction is the same as that of the wind with which they 

 are associated. A study of the prevailing winds for the lake stations, 

 made by the officials of the Weather Bureau and covering a period of 

 seventeen years, shows that there were on the average 6Q per cent of 

 westerly winds for the whole year. For the months from May to Sep- 

 tember 56 per cent weit from a westerly direction. For the same period 

 of time a study of the resultant wind directions shows that in 183 out 

 of 204 monthly values and in all the annual values the resultant is 

 westerly. 



The occurrence of undercurrents in a direction contrary to that of the 

 surface current or of the prevailing wind is a common feature. Mr 

 L. J. Clarke * found some interesting examples of these currents off 

 Toronto when making investigations of the lake currents in tliat vicinity. 

 Mr Clarke also mentions that fishermen at Niagara, New York, found 



♦Transactions of the Canadian Institute, vol. il, 1890, pp. 154-157, and vol. Ill, 1891, 

 pp. 275-281. 



